1. Field of the Invention
The present invention relates to a color cathode-ray tube and a method of manufacturing the same and, more particularly, to a color cathode-ray tube in which filter films are disposed between the inner surface of a face panel and phosphor films, and a method of manufacturing the same.
2. Description of the Prior Art
FIG. 1 is a sectional view of the main part of a color cathode-ray tube. As shown in FIG. 1, the outer shape of a color cathode-ray tube 1 consists of a face panel 2 and a funnel 15. A black matrix film 3 and filter films 7 are formed on the inner surface of the face panel 2. The filter films 7 are formed at positions where light-transmitting windows 4 are located. Red, blue, and green phosphor films 8 are formed on the inner surfaces of the filter films 7. The color cathode-ray tube 1 also comprises a shadow mask 9, an electron gun 16, and a deflection coil 17. The shadow mask 9 is arranged at a position slightly remote from the phosphor films 8 to oppose them. The electron gun 16 emits electrons. The deflection coil 17 controls the paths of the electrons.
In recent years, as personal computers spread widely, market requirements for high resolution, high luminance, and the like become more and more intense. In particular, since the graphic display function has become substantial, a further increase in color purity is demanded. As a means for increasing the color purity, a technique for arranging color filter films corresponding to the emission colors of phosphors between the face panel and phosphor films is introduced, as described in Journal of Electrochemical Society, Vol. 28, No. 11 (1981).
FIGS. 2A to 2I are views for explaining the conventional process in the manufacture of filter films and phosphor films. The steps of forming a blue filter film and blue phosphor film will be described as an example.
FIG. 2A is a sectional view showing a state wherein a black matrix film 3 (to be referred to as a BM film hereinafter) and light-transmitting windows 4 are formed on the inner surface of a face panel 2 in advance.
As shown in FIG. 2B, a blue filter solution is applied to cover the BM film 3 and light-transmitting windows 4, to such a degree that the BM film 3 and the face panel 2 sink slightly, and is dried, to form a blue filter layer 7b on the entire surface of the face panel 2.
As shown in FIG. 2C, only a required portion, i.e., a desired light-transmitting window 4, of the blue filter layer 7b is exposed with ultraviolet light 10 through a shadow mask 9.
As shown in FIG. 2D, since only the exposed portion is water-insoluble, when development is performed with water, other portions that are not exposed are removed, and a desired blue filter film 7B is formed in only the exposed light-transmitting window 4.
Similarly, a green filter film 7G and a red filter film 7R are sequentially formed, as shown in FIG. 2E. In this manner, the desired filter films 7G, 7B, and 7R are formed at predetermined positions on the inner surface of the face panel 2, i.e., in the light-transmitting windows 4.
Phosphor films are formed by coating on the corresponding filter films 7G, 7B, and 7R that are formed with the above method. How to form a blue phosphor film 8B will be described.
As shown in FIG. 2F, a blue phosphor slurry is applied to the upper surfaces of the filter films 7G, 7B, and 7R formed on the inner surface of the face panel 2, and is dried to form a blue phosphor layer 8b.
As shown in FIG. 2G, only a required portion of the blue filter layer 8b, i.e., the upper surface portion of the blue filter film 7B formed in the above step, is exposed with ultraviolet light 10 through the shadow mask 9.
As shown in FIG. 2H, since only the exposed portion is water-insoluble, when development is performed with water, other portions that are not exposed are removed, and only a desired blue phosphor film 8B that is exposed is formed as it is stacked on the blue filter film 7B.
Similarly, a green phosphor film 8G and a red phosphor film 8R are sequentially formed, as shown in FIG. 2I. In this manner, the phosphor films 8B, 8G, and 8R are formed at predetermined positions on the inner surface of the face panel 2, i.e., such that they are stacked on the filter films 7B, 7G, and 7R, respectively.
As described above, the color cathode-ray tube manufacturing method requires two exposing steps, i.e., one in the filter film forming step of forming the filter films 7B (7G, 7R) and one in the phosphor film forming step of forming the phosphor films 8B (8G, 8R) by stacking them on the filter films 7B (7G, 7R). Due to misalignment between the face panel 2 and the shadow mask 9 and the like, a displacement sometimes occurs between the filter films 7B (7G, 7R) and the phosphor films 8B (8G, 8R). For example, if the green phosphor films 8G are exposed to extend onto the adjacent blue filter films 7B, color mixture occurs to degrade the color purity. Despite that the step of forming the respective filter films and the step of forming the phosphor films are basically identical, these similar steps must be provided as two steps, leading to a very high manufacturing cost.
As a means for solving these problems, for example, Japanese Unexamined Patent Publication No. 6-295683 discloses the following technique. Water-soluble polymers having different cloudy points are used as the base polymers of the filter slurry and the phosphor slurry. A filter layer is formed of the filter slurry having the first cloudy point, and the phosphor layer is formed on it using the phosphor slurry having the second cloudy point. Thereafter, exposure is performed once to eliminate misalignment between filter films and phosphor films.
With this technique, although the entire process is shortened when compared to the conventional manufacturing method, additional steps may be required in accordance with the cloudy point, temperature control must be performed in the process, and factors that largely influence the fraction nondefective may be present.